U.S. patent number 7,305,207 [Application Number 11/062,609] was granted by the patent office on 2007-12-04 for cleaning system.
This patent grant is currently assigned to Sharp Kabushiki Kaisha. Invention is credited to Yoshie Iwakura, Susumu Murakami, Kuniaki Nakano.
United States Patent |
7,305,207 |
Murakami , et al. |
December 4, 2007 |
Cleaning system
Abstract
A cleaning system includes a rotating member and a cleaning
blade which is forced against a curved outer surface of the
rotating member to scrape off matter to be removed (toner) which is
present along the outer surface of the rotating member. The
cleaning blade has greater hardness than the outer surface of the
rotating member.
Inventors: |
Murakami; Susumu (Soraku-gun,
JP), Iwakura; Yoshie (Higashiosaka, JP),
Nakano; Kuniaki (Soraku-gun, JP) |
Assignee: |
Sharp Kabushiki Kaisha
(Osaka-shi, JP)
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Family
ID: |
34836459 |
Appl.
No.: |
11/062,609 |
Filed: |
February 22, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050180785 A1 |
Aug 18, 2005 |
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Foreign Application Priority Data
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Feb 23, 2004 [JP] |
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2004-046542 |
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Current U.S.
Class: |
399/297; 399/327;
399/343; 399/350 |
Current CPC
Class: |
G03G
15/168 (20130101); G03G 2215/0119 (20130101) |
Current International
Class: |
G03G
15/16 (20060101) |
Field of
Search: |
;399/297,302,308,327,343,350 ;15/256.5,256.51 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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4-362680 |
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Dec 1992 |
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JP |
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5-307346 |
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Nov 1993 |
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JP |
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8-137298 |
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May 1996 |
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JP |
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2002-62740 |
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Feb 2002 |
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JP |
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2002-148958 |
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May 2002 |
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JP |
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2002-278308 |
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Sep 2002 |
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JP |
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Primary Examiner: Tran; Hoan
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Claims
What is claimed is:
1. A cleaning system comprising: a rotating member; and a cleaning
blade which is forced against a curved outer surface of said
rotating member to scrape off matter to be removed which is present
along the outer surface of said rotating member, said cleaning
blade having greater hardness than the outer surface of said
rotating member such that the outer surface of the rotating member
becomes a substantially flat region when the cleaning blade is
forced against the outer surface of the rotating member.
2. The cleaning system according to claim 1, wherein said cleaning
blade has stiffness high enough to maintain an original shape when
forced against said rotating member, and said rotating member has
flexibility which allows a portion of the outer surface of said
rotating member pressed by said cleaning blade to become recessed
due to a pushing force exerted by said cleaning blade.
3. The cleaning system according to claim 1, wherein at least a
pushing part of said cleaning blade contains fluorine.
4. The cleaning system according to claim 1, wherein said rotating
member suspends an endless belt under tension and said cleaning
blade is forced against the outer surface of said rotating member
via said endless belt to scrape off the matter to be removed which
is present along an outer surface of said endless belt.
5. The cleaning system according to claim 1, wherein said rotating
member suspends under tension an endless-belt-type photosensitive
member having an outer surface on which a toner image is created
from an electrostatic latent image which is formed based on
differences in electrostatic potential imparted to the outer
surface of said photosensitive member, and said cleaning blade is
forced against the outer surface of said rotating member via said
photosensitive member to scrape off the matter to be removed which
is present along the outer surface of said photosensitive
member.
6. The cleaning system according to claim 1, wherein said rotating
member is a fuser roller for firmly fixing a toner image loosely
adhering to a recording medium onto the recording medium.
7. A cleaning system comprising: an endless belt having an outer
surface to which matter to be removed adheres; a roller device
which suspends and turns said endless belt under tension; and a
cleaning blade which is forced against a portion of the outer
surface of said endless belt where said endless belt is not
supported from an inside surface thereof by said roller device,
said cleaning blade being located proximate to the roller device,
said cleaning blade having stiffness high enough to maintain an
original shape when forced against said endless belt; wherein said
endless belt turns under conditions in which a portion of said
endless belt forced by said cleaning blade becomes displaced in the
direction of a normal to said forced portion of said endless belt
due to a pushing force exerted by said cleaning blade.
8. The cleaning system according to claim 7, wherein said roller
device includes a driving roller and a driven roller, said endless
belt turns along a looping path which passes through a primary
image transfer area where a toner image is transferred onto said
endless belt from an image carrying member, a nearby area of said
driving roller where the toner image is transferred onto a
recording medium and a nearby area of said driven roller in this
order, and said cleaning blade presses against said endless belt at
a particular location within a range from the nearby area of said
driving roller to the nearby area of said driven roller in the
looping path of said endless belt.
9. The cleaning system according to claim 7, wherein said endless
belt is an endless-belt-type photosensitive member having an outer
surface on which a toner image is created from an electrostatic
latent image which is formed based on differences in electrostatic
potential imparted to the outer surface of said photosensitive
member, and said cleaning blade is forced against the outer surface
of said roller device via said photosensitive member to scrape off
the matter to be removed which is present along the outer surface
of said photosensitive member.
Description
CROSS REFERENCE
This Nonprovisional application claims priority under 35 U.S.C.
.sctn. 119(a) on Patent Application No. 2004-046542 filed in Japan
on Feb. 23, 2004, the entire contents of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning system including a
cleaning blade for scraping off matter to be removed from an outer
surface of a rotating member.
An image forming apparatus is provided with a photosensitive drum,
an intermediate transfer belt, a fuser roller and a cleaning
system, for example. A toner image is formed on an outer surface of
the photosensitive drum based on an electrostatic latent image
which is formed from image data input into the image forming
apparatus. The toner image formed on the photosensitive drum is
transferred onto the intermediate transfer belt. The toner image
transferred onto the intermediate transfer belt is then transferred
onto a sheet of printing paper and fused, or fixed, thereto by the
fuser roller. The cleaning system removes residual toner left on
such rotating members as the photosensitive drum and the
intermediate transfer belt to prevent deterioration of image
quality in succeeding processes.
FIG. 1 is a structural diagram schematically showing an example of
a conventional cleaning system including a cleaning blade 103. As
depicted in FIG. 1, an endless belt 101 is mounted over a rigid
rotating body (photosensitive drum) 102. As the cleaning blade 103
having flexibility is pressed toward a cylindrical outer surface of
the rotating body 102 with the endless belt 101 passing in between,
the cleaning blade 103 scrapes off matter to be removed, i.e.,
residual toner, left on an outer surface of the turning endless
belt 101. If the cleaning blade 103 which scrapes across the
endless belt 101 turning on the rigid rotating body 102 is an
element made of a rigid material, the cleaning blade 103 will
damage the endless belt 101. For this reason, the hardness of the
cleaning blade 103 is made lower than that of the outer surface of
the rotating body 102. Therefore, a tip end of the cleaning blade
103 could be crushed by a pushing force applied thereto against the
outer surface of the rotating body 102.
FIGS. 2A to 2D are explanatory diagrams showing how the
conventional cleaning system works. Forced in tight contact with
the outer surface of the endless belt 101, the cleaning blade 103
scrapes and collects toner powder adhering to the outer surface of
the endless belt 101 as shown in FIG. 2A. The tip end of the
cleaning blade 103 is pulled in a turning direction (clockwise
direction as illustrated) of the rotating body 102 due to a
frictional force exerted between the endless belt 101 and the
cleaning blade 103 as shown in FIG. 2B. When the frictional pulling
force exerted on the cleaning blade 103 by the endless belt 101 in
the turning direction of the rotating body 102 exceeds a limit of
buckling strength of the cleaning blade 103, the tip end of the
cleaning blade 103 bounces back due to its resilience and flips off
the cumulated toner powder as shown in FIG. 2C, and then the
cleaning blade 103 returns to an original position as shown in FIG.
2D. The cleaning blade 103 removes the residual toner while
repeatedly producing the aforementioned action due to a so-called
stick-slip phenomenon.
Therefore, the conventional cleaning system is associated with a
problem that surrounding areas of the cleaning blade 103 are apt to
be contaminated with the toner powder scattered around by the
stick-slip phenomenon. Furthermore, since great pressure is applied
to the cleaning blade 103, the tip end of the cleaning blade 103
tends to wear or be cut away. The outer surface of the endless belt
101 with which the cleaning blade 103 is forced in tight contact is
likely to wear or be abraded. In addition, the pressing cleaning
blade 103 is prone to cause meandering of the endless belt 101.
If the endless belt 101 exerts too large a friction force on the
cleaning blade 103, the tip end of the cleaning blade 103 would
occasionally become bent in an opposite direction as shown by
broken lines in FIG. 3. When the tip end of the cleaning blade 103
is bent in the opposite direction as illustrated, the cleaning
blade 103. will not be able to remove the toner. Typically, a slip
agent 104 made of fine spherical plastic particles is applied to
the outer surface of the endless belt 101 as shown in FIG. 4 in the
conventional cleaning system. The slip agent 104 serves to prevent
such backward bending of the cleaning blade 103 as mentioned above
(FIG. 3). In addition, fine particles of an external additive 106
made of silica and magnetite are attached to an outer surface of
each toner particle 105.
Each particle of the slip agent 104 is approximately 0.3
micrometers in diameter while each particle of the external
additive 106 has a diameter smaller than that of the slip agent
104. Since the outer surface of the rotating body 102, against
which the cleaning blade 103 forces the endless belt 101, has a
surface roughness of approximately 50 micrometers, the particles of
both the slip agent 104 and the external additive 106 pass through
a gap between the rotating body 102 and the cleaning blade 103.
The particles of the slip agent 104 and the external additive 106
passing between the rotating body 102 and the cleaning blade 103
act as abrasive material, which accelerates wear of the endless
belt 101 against which the cleaning blade 103 is tightly pressed.
In a case where the cleaning system is used for cleaning a
photosensitive drum, those particles of the slip agent 104 and the
external additive 106 applied to each toner particle 105 which have
passed between the photosensitive drum and the tip end of the
cleaning blade 103 would adhere to a charging wire for
electrostatically charging the photosensitive drum, thereby causing
uneven tones of a printed image.
An example of a cleaning system employing a cleaning blade is found
in Japanese Patent Application Publication No. 1992-362680. The
Publication discloses an arrangement for preventing backward
bending of the cleaning blade which is pressed against an image
transfer belt with the aid of an elastic reinforcing plate which
has higher stiffness than the cleaning blade and is disposed in
contact with the cleaning blade on a rear side thereof.
Another example of a cleaning system employing a cleaning blade is
found in Japanese Patent Application Publication No. 2002-148958.
This Publication also discloses an arrangement for preventing
deformation (backward bending) of the cleaning blade. In this
arrangement, an image transfer belt has a double-layer structure
including a base layer having high flexibility and a surface layer
formed by heat-bonding a plastic film to the base layer to provide
improved lubricity between the cleaning blade and the image
transfer belt.
The aforementioned prior art arrangements disclosed in Japanese
Patent Application Publication Nos. 1992-362680 and 2002-148958 are
approaches to preventing backward bending of the cleaning blade.
Accordingly, neither of these arrangements prevents the
aforementioned problems of the prior art, such as contamination of
the surrounding areas of the cleaning blade 103 by the toner powder
scraped off and scattered around, wear or cutting of the tip end of
the cleaning blade 103, wear of the endless belt 101 and uneven
tones of a printed image caused by those particles of the slip
agent 104 and the external additive 106 which have passed between
the photosensitive drum and the tip end of the cleaning blade
103.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a cleaning system which
can remove fine particles, such as toner powder, and prevent
scattering of the removed particles. It is another object of the
invention to provide a cleaning system of which cleaning blade can
be used for an extended period of time.
According to the invention, a cleaning system includes a rotating
member and a cleaning blade. Forced against a curved outer surface
of the rotating member, the cleaning blade slides along the outer
surface of the rotating member and scrapes off matter to be removed
which is present along the outer surface of the rotating member.
The cleaning blade has greater hardness than the outer surface of
the rotating member. Since the hardness of the cleaning blade is
higher than that of the rotating member, the cleaning blade can
scrape off the matter to be removed without producing the
stick-slip phenomenon.
These and other objects of the invention will become more readily
apparent from the following description when read in conjunction
with accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a structural diagram schematically showing a conventional
cleaning system;
FIGS. 2A, 2B, 2C and 2D are explanatory diagrams showing how the
conventional cleaning system works;
FIG. 3 is an explanatory diagram showing a situation in which a
cleaning blade of the conventional cleaning system has become bent
in an opposite direction;
FIG. 4 is an enlarged view particularly showing a portion where the
cleaning blade of the conventional cleaning system presses against
a rotating body;
FIG. 5 is a sectional diagram schematically showing the structure
of an image forming apparatus employing a cleaning system according
to an embodiment of the invention;
FIG. 6 is a schematic diagram showing an image transfer unit and a
cleaning unit of the embodiment;
FIG. 7 is an enlarged view of a nearby area of a driven roller;
and
FIG. 8 is a sectional diagram schematically showing the structure
of a cleaning system according to another embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
Specific embodiments of the invention are now described with
reference to the accompanying drawings.
FIG. 5 is a sectional diagram schematically showing the structure
of an image forming apparatus 1 employing a cleaning system
according to a preferred embodiment of the invention. Having a
full-color mode and a monochrome mode, the image forming apparatus
1 including the cleaning system of the embodiment forms multicolor
or monochrome images on sheets of a recording medium, such as
printing paper, according to externally supplied image data. To
perform such image forming operation, the image forming apparatus 1
includes an exposure unit 13, four photosensitive drums 3A to 3D
serving as image carrying members, four charging rollers 5A to 5D,
four developing units 2A to 2D, four cleaning units 4A to 4D, an
intermediate image transfer belt (endless belt) 7, four primary
image transfer rollers 6A to 6D, a secondary image transfer roller
11, a fuser unit 12, sheet transport paths S1, S2 and S3, a paper
cassette 10, a manual feed tray 20 and a delivery tray 15.
The photosensitive drum 3A, the charging roller 5A, the developing
units 2A and the cleaning unit 4A together constitute an image
forming section PA. Similarly, the photosensitive drum 3B, the
charging roller 5B, the developing units 2B and the cleaning unit
4B together constitute an image forming section PB. The
photosensitive drum 3C, the charging roller 5C, the developing
units 2C and the cleaning unit 4C together constitute an image
forming section PC. The photosensitive drum 3D, the charging roller
5D, the developing units 2D and the cleaning unit 4D together
constitute an image forming section PD.
The four image forming sections PA, PB, PC, PD perform image
forming operation by using image data corresponding to black, cyan,
magenta and yellow, respectively. The image forming sections PA,
PB, PC, PD are arranged in line along a turning direction
(sub-scanning direction) of the intermediate image transfer belt
7.
The charging rollers 5A to 5D are contact-type charging devices for
uniformly charging cylindrical outer surfaces of the photosensitive
drums 3A to 3D to a specified potential level. As an alternative,
contact charging devices using charging brushes or noncontact
charging devices using charging wires may be employed instead of
the charging rollers 5A to 5D.
Including a semiconductor laser, a polygon mirror and reflecting
mirrors which are not illustrated, the exposure unit 13 projects
laser beams based on the image data corresponding to the four
colors (black, cyan, magenta, yellow) upon the respective
photosensitive drums 3A to 3D. As a result, latent images carrying
black, cyan, magenta and yellow components are formed on the outer
surfaces of the photosensitive drums 3A to 3D, respectively,
according to the image data for the four color components.
The developing units 2A to 2D store black, cyan, magenta and yellow
toners, respectively, and supply these toners onto the outer
surfaces of the photosensitive drums 3A to 3D to convert the
respective latent images into toner images of the individual colors
(including black). The cleaning units 4A to 4D remove and collect
residual toners left on the outer surfaces of the respective
photosensitive drums 3A to 3D upon completion of a toner image
transfer process.
There is provided an image transfer unit 8 above the photosensitive
drums 3A to 3D. The image transfer unit 8 includes the intermediate
image transfer belt 7, a driving roller 71, a driven roller
(rotating member) 72, a tension roller 17, the primary image
transfer rollers 6A to 6D and a cleaning unit 9 for cleaning the
intermediate image transfer belt 7.
The intermediate image transfer belt 7 is an endless belt measuring
75 to 150 micrometers thick. Mounted between the driving roller 71
and the driven roller 72, the intermediate image transfer belt 7
turns in the clockwise direction as illustrated in FIG. 5. The
photosensitive drum 3D, the photosensitive drum 3C, the
photosensitive drum 3B and the photosensitive drum 3A are arranged
in this order along the turning direction of the intermediate image
transfer belt 7, facing from below an outer surface of the
intermediate image transfer belt 7 at a bottom half thereof.
The primary image transfer rollers 6A to 6D are located face to
face with the photosensitive drums 3A to 3D, respectively, with the
bottom half of the intermediate image transfer belt 7 passing in
between. Each of the primary image transfer rollers 6A to 6D
includes a round bar made of a metallic material, such as stainless
steel, measuring 8 to 10 millimeters in diameter of which curved
outer surface is covered with an electrically conductive elastic
material, such as ethylene-propylene-diene terpolymer (EPDM) or
urethane foam. As an alternative, brush-shaped intermediate image
transfer members may be used instead of the primary image transfer
rollers 6A to 6D.
An image transfer bias (or electrostatic potential) of a polarity
opposite to that of a static charge (negative in this embodiment)
given to the toners is applied to the primary image transfer
rollers 6A to 6D, while the intermediate image transfer belt 7 is
uniformly charged to a high voltage by means of an electrically
conductive elastic member. With this arrangement, the color toner
images formed on the individual photosensitive drums 3A to 3D are
successively transferred one on top of another onto the outer
surface of the intermediate image transfer belt 7 to produce a
full-color toner image on the outer surface of the intermediate
image transfer belt 7.
If image data for only part of the four color components (black,
cyan, magenta, yellow) has been input, however, the latent image(s)
and the toner image(s) are formed only on the photosensitive
drum(s), among the four photosensitive drums 3A to 3D, for which
the image data has been input. When the monochrome mode is
selected, for example, the latent image and the toner image are
formed only on the photosensitive drum 3A for black and only the
black toner image is transferred onto the outer surface of the
intermediate image transfer belt 7.
As the intermediate image transfer belt 7 turns, the toner image
formed on the outer surface of the intermediate image transfer belt
7 as discussed above is brought to a position facing the secondary
image transfer roller 11. While the image forming apparatus 1 is
performing the image forming operation, the secondary image
transfer roller 11 is pressed against the outer surface of the
intermediate image transfer belt 7 with a specified level of
nipping pressure. When a sheet of printing paper fed from the paper
cassette 10 or the manual feed tray 20 passes between the secondary
image transfer roller 11 and the driving roller 71, a high voltage
of a polarity (positive in this embodiment) opposite to that of the
static charge (negative in this embodiment) given to the toners is
applied to the secondary image transfer roller 11. As a result, the
toner image is transferred from the outer surface of the
intermediate image transfer belt 7 onto a surface of the sheet.
To maintain the specified level of nipping pressure between the
secondary image transfer roller 11 and the intermediate image
transfer belt 7, one of the secondary image transfer roller 11 and
the driving roller 71 is made of a rigid material (e.g., metal)
while the other is an elastic roller made of an elastic material
(e.g., rubber or plastic foam).
Located at a position facing the driven roller 72 via the
intermediate image transfer belt 7, the cleaning unit 9 removes and
collects unused masses of the toners transferred from the
photosensitive drums 3A to 3D onto the intermediate image transfer
belt 7, that is, residual toner powder left on the intermediate
image transfer belt 7 without being transferred onto the sheet of
printing paper. The cleaning unit 9 working in this way serves to
prevent color mixing in a succeeding image forming job. In this
embodiment, the cleaning system of this invention is implemented as
a system for removing the residual toner remaining on the
intermediate image transfer belt 7 as will be later discussed in
further detail.
The sheet on which the toner image has been transferred is guided
to the fuser unit 12 which includes a heat roller 31 and a pressure
roller 32. Pressing against each other with a specific pushing
force, the heat roller 31 and the pressure roller 32 rotate
together while squeezing the sheet in between. As the heat roller
31 and the pressure roller 32 apply heat and pressure to the sheet,
the toner image is firmly fixed, or fused, onto the surface of the
sheet. Then, the sheet carrying the fused toner image is discharged
onto the delivery tray 15 by a pair of transport rollers 25B and a
pair of delivery rollers 18
The image forming apparatus 1 has the aforementioned sheet
transport path S1 which extends generally vertically for
successively feeding sheets of printing paper stored in the paper
cassette 10 upward between the secondary image transfer roller 11
and the intermediate image transfer belt 7 and through the fuser
unit 12 onto the delivery tray 15.
Along this sheet transport path S1, there are provided a pickup
roller 16A for pulling and feeding each successive sheet into the
sheet transport path S1 out of the paper cassette 10, transport
rollers 25A for feeding the sheet pulled out of the paper cassette
10 upward along the sheet transport path S1, a pair of registration
rollers 14 for temporarily halting the sheet transported along the
sheet transport path S1 and advancing the sheet with proper timing
to a secondary image transfer area B (see FIG. 6) located between
the secondary image transfer roller 11 and the intermediate image
transfer belt 7, as well as the aforementioned transport rollers
25B and delivery rollers 18 for ejecting the sheet onto the
delivery tray 15.
Also formed inside the image forming apparatus 1 is the
aforementioned sheet transport path S2 extending from the manual
feed tray 20 to the registration roller pair 14. There are provided
a pickup roller 16B and pairs of transport rollers 25C, 25D and 25E
along the sheet transport path S2. Further, the aforementioned
sheet transport path S3 is formed in the image forming apparatus 1
between the registration roller pair 14 and the delivery roller
pair 18 with pairs of transport rollers 25F and 25G provided along
the sheet transport path S3.
The delivery rollers 18 are supported rotatably in both forward and
reverse turning directions. In a single-sided image forming mode in
which an image is formed on only one side of a sheet, the image
forming apparatus 1 causes the delivery rollers 18 to turn in the
forward turning direction to eject the sheet onto the delivery tray
15 when the image has been printed on one side of the sheet. In a
duplex (double-sided) image-forming mode in which first and second
images are formed on front and reverse sides of a sheet,
respectively, the image forming apparatus 1 causes the delivery
rollers 18 to turn in the forward turning direction to eject the
sheet onto the delivery tray 15 when the second image has been
printed on the reverse side of the sheet.
When printing the first image on the front side of the sheet in the
duplex image-forming mode, on the other hand, the image forming
apparatus 1 causes the delivery rollers 18 to turn in the forward
turning direction until a trailing edge of the sheet passes between
the transport rollers 25B. Then, when the delivery rollers 18 nip
the trailing edge of the sheet, the image forming apparatus 1
causes the delivery rollers 18 to turn in the reverse turning
direction to guide the sheet into the sheet transport path S3.
Consequently, the sheet carrying the first image printed on one
side (front side) only is guided back into the sheet transport path
S1 with the front and reverse sides, and leading and trailing
edges, of the sheet reversed.
The registration rollers 14 advance the sheet fed from the paper
cassette 10 or the manual feed tray 20, or fed back into the sheet
transport path S1 through the sheet transport path S3, to the
secondary image transfer area B located between the secondary image
transfer roller 11 and the intermediate image transfer belt 7 with
specific timing. Specifically, the registration rollers 14 halt in
a standby state while gripping the leading edge of the sheet just
before the intermediate image transfer belt 7 begins to turn again.
The registration rollers 14 are caused to begin rotating again with
such timing that the leading edge of the sheet aligns with a
forward end of the toner image formed on the intermediate image
transfer belt 7 (more exactly a leading edge of an image forming
area on the intermediate image transfer belt 7) at the secondary
image transfer area B where the secondary image transfer roller 11
presses against the intermediate image transfer belt 7.
FIG. 6 is a schematic diagram showing the image transfer unit 8 and
the cleaning unit 9. The intermediate image transfer belt 7 is
mounted generally horizontally between the driving roller 71 and
the driven roller 72. The intermediate image transfer belt 7 moves
along a looping path which passes through a primary image transfer
area A where the color toner images formed on the individual
photosensitive drums 3A to 3D are transferred therefrom onto the
outer surface of the intermediate image transfer belt 7, the
aforementioned secondary image transfer area (nearby area of the
driving roller 71) B where the toner image transferred onto the
intermediate image transfer belt 7 is transferred onto a sheet of
printing paper between the secondary image transfer roller 11 and
the driving roller 71, and a nearby area C of the driven roller 72
where the intermediate image transfer belt 7 is pulled by the
driven roller 72.
In this embodiment, the primary image transfer roller 6A is
positioned in such a manner that the center of a contact area
between the primary image transfer roller 6A and the intermediate
image transfer belt 7 is located on a downstream side of the center
of a contact area between the photosensitive drum 3A and the
intermediate image transfer belt 7 with respect to the turning
direction of the intermediate image transfer belt 7. The other
primary image transfer rollers 6B to 6D are also positioned in a
similar way relative to the respective photosensitive drums 3B to
3D. It is to be noted, however, that arrangement of the primary
image transfer rollers 6A to 6D and the photosensitive drums 3A to
3D is not limited to this relationship in their locations.
The tension roller 17 is forced against an inner surface of the
intermediate image transfer belt 7 as illustrated in FIG. 6 to
produce a specific tension acting upward from inside on the
intermediate image transfer belt 7 between the secondary image
transfer area B and the nearby area C of the driven roller 72 in
the looping path of the intermediate image transfer belt 7.
The cleaning unit 9 is located at the position facing the driven
roller 72 with the intermediate image transfer belt 7 in between as
mentioned earlier. The cleaning unit 9 includes a housing 91 and a
cleaning blade 92.
FIG. 7 is an enlarged view of the nearby area C of the driven
roller 72. The driven roller 72 pulls the intermediate image
transfer belt 7 at one end. As illustrated in FIG. 7, the residual
toner powder left on the intermediate image transfer belt 7 after a
toner image transfer process at the secondary image transfer area B
remains attached to the outer surface of the intermediate image
transfer belt 7. The cleaning blade 92 is forced against a
cylindrical outer surface of the driven roller 72 at an acute angle
with the intermediate image transfer belt 7 passing in between. A
tip end of the cleaning blade 92, or a scraping edge of the
cleaning blade 92 which is held in contact with the intermediate
image transfer belt 7, has a surface layer made of fluoroplastic to
give enhanced lubricity to the tip end of the cleaning blade
92.
The tip end of the cleaning blade 92 has greater hardness than the
outer surface of the driven roller 72. In this embodiment, the tip
end of the cleaning blade 92 has a hardness of 70 or above as
measured according to the Japanese Industrial Standard (JIS) Asker
C hardness scale. Preferably, the hardness of the tip end of the
cleaning blade 92 is 75 to 80. The outer surface of the driven
roller 72 has an Asker C hardness of 65 or less, more preferably,
45 to 55.
In this structure, the cleaning blade 92 maintains its shape
without deforming when pressed against the outer surface of the
driven roller 72. When pressed by the cleaning blade 92, a contact
area of the outer surface of the driven roller 72 forced by the
cleaning blade 92 becomes slightly recessed due to a pushing force
exerted by the cleaning blade 92. When the tip end of the cleaning
blade 92 presses the outer surface of the driven roller 72 in this
fashion, the cleaning blade 92 can scrape off the residual toner
powder from the intermediate image transfer belt 7 without
producing the earlier-mentioned stick-slip phenomenon.
When pressed by the cleaning blade 92, a portion of the outer
surface of the driven roller 72 forced by the cleaning blade 92 is
depressed by approximately 0.1 mm in the direction of a central
axis of the driven roller 72 due to the pushing force exerted by
the cleaning blade 92. Since the driven roller 72 has a surface
roughness of approximately 50 micrometers, the outer surface of the
driven roller 72 is pushed in by the pushing force of the cleaning
blade 92 by an amount larger than the surface roughness of the
driven roller 72. Thus, when the cleaning blade 92 presses the
outer surface of the driven roller 72, the portion of the outer
surface of the driven roller 72 forced by the cleaning blade 92
becomes generally a geometrically flat region without creating
conspicuous furrows or ridges. Accordingly, the intermediate image
transfer belt 7 is forced by the cleaning blade 92 against this
geometrically almost flat region of the outer surface of the driven
roller 72 and, therefore, matter adhering to the intermediate image
transfer belt 7, such as the residual toner left thereon, can not
pass through a gap between the intermediate image transfer belt 7
and the cleaning blade 92 but is scraped off by the cleaning blade
92. Even if a slip agent is applied to the outer surface of the
intermediate image transfer belt 7 or fine particles of an external
additive are attached to an outer surface of each toner particle,
such substances constituting matter to be removed are scraped off
by the cleaning blade 92.
Furthermore, because the tip end of the cleaning blade 92 is
covered with a fluoroplastic layer for enhanced lubricity, it is no
longer absolutely necessary to apply a slip agent to the outer
surface of the intermediate image transfer belt 7.
Even when the cleaning blade 92 is forced against the driven roller
72, the tip end of the cleaning blade 92 does neither crush nor
produce the stick-slip phenomenon. This serves to significantly
suppress wear and cutting away of the scraping edge of the cleaning
blade 92 which is held in contact with the driven roller 72,
thereby extending the useful life of the cleaning blade 92.
As the cleaning blade 92 scrapes off the residual toner from the
outer surface of the intermediate image transfer belt 7 without
producing the stick-slip phenomenon, it is possible to suppress
scattering of the toner powder and minimize contamination of
surrounding areas of the cleaning blade 92 with the toner
powder.
Furthermore, since the driven roller 72 has flexibility which
allows the driven roller 72 to become recessed when forced by the
cleaning blade 92, the intermediate image transfer belt 7 is not
damaged by the pushing force exerted by the cleaning blade 92. In
addition, the cleaning blade 92 is not so hard as metal but has
proper flexibility and the tip end of the cleaning blade 92 has
enhanced lubricity. This further ensures that the intermediate
image transfer belt 7 would not be damaged by the pushing force
exerted by the cleaning blade 92.
Moreover, the enhanced lubricity of the tip end of the cleaning
blade 92 serves to reduce frictional force between the cleaning
blade 92 and the intermediate image transfer belt 7. Also, the
cleaning blade 92 is formed to have a specific degree of stiffness,
making it possible to prevent the cleaning blade 92 from bending in
an opposite direction. Accordingly, the cleaning blade 92 of the
embodiment can remove the residual toner powder and other
contaminants whatever left on the outer surface of the intermediate
image transfer belt 7 in a reliable fashion.
The cleaning system of the present embodiment thus far described
may be implemented as a cleaning system for removing residual toner
from the heat roller 31 or the pressure roller 32 of the fuser unit
12 for fusing the toner image onto a sheet of printing paper. In
this varied form of the embodiment, a cleaning blade is forced
against the heat roller 31 or the pressure roller 32. Since the
cleaning blade of this variation does not produce the stick-slip
phenomenon either, scattering of the toner is prevented in the same
fashion as discussed above. In this variation of the embodiment,
the heat roller 31 or the pressure roller 32 corresponds to a fuser
roller referred to in the appended claims.
FIG. 8 is a sectional diagram schematically showing the structure
of a cleaning system according to another embodiment of the
invention. In this embodiment, the intermediate image transfer belt
7 is suspended between the driving roller 71 and the driven roller
72 as well. Residual toner powder constituting matter to be removed
remains attached to the outer surface of the intermediate image
transfer belt 7 after a toner image transfer process at the
secondary image transfer area B. A cleaning blade 92A of this
embodiment is forced against a portion of the outer surface of the
intermediate image transfer belt 7 where the intermediate image
transfer belt 7 is not supported from its inside surface by the
driving roller 71, the driven roller 72, the tension roller 17, or
else. The cleaning blade 92A is forced against the outer surface of
the intermediate image transfer belt 7 at an acute angle. In this
embodiment, the cleaning blade 92A is located apart from but in
close proximity to the driven roller 72 as illustrated in FIG. 8.
Since the cleaning blade 92A is located so close to the driven
roller 72 where the driven roller 72 does not flutter too much that
the cleaning blade 92A removes the residual toner on the
intermediate image transfer belt 7 in a reliable fashion.
The cleaning blade 92A may press against the intermediate image
transfer belt 7 at any appropriate location within a range from the
secondary image transfer area B to the nearby area C of the driven
roller 72 in the looping path of the intermediate image transfer
belt 7. Preferably, however, the cleaning blade 92A presses against
the intermediate image transfer belt 7 at a convenient location
within a range from the secondary image transfer area B to the
nearby area C of the driven roller 72. More preferably, the
cleaning blade 92A presses against the intermediate image transfer
belt 7 at a location in close proximity to one of the driving
roller 71, the driven roller 72 and the tension roller 17 around
which the intermediate image transfer belt 7 is mounted.
As in the foregoing embodiment, a tip end of the 92A has a hardness
of 70 or above, preferably 75 to 80, as measured by the JIS Asker C
hardness scale. Therefore, the cleaning blade 92A retains its shape
without deforming when pressed against the outer surface of the
intermediate image transfer belt 7. The tip end of the cleaning
blade 92A, or a scraping edge of the cleaning blade 92A which is
held in contact with the intermediate image transfer belt 7, also
has a surface layer made of fluoroplastic to give enhanced
lubricity to the tip end of the cleaning blade 92A.
When pressed by the cleaning blade 92A, a portion of the
intermediate image transfer belt 7 forced by the cleaning blade 92A
becomes displaced in the direction of a normal to the forced
portion of the intermediate image transfer belt 7, or in the
direction perpendicular to the outer surface of the intermediate
image transfer belt 7, due to a pushing force exerted by the
cleaning blade 92A. The amount of this displacement is
approximately 0.5 millimeters. There exists no mechanical part
located to face the cleaning blade 92A via the intermediate image
transfer belt 7 when the intermediate image transfer belt 7 is
forced by the cleaning blade 92A. Therefore, the intermediate image
transfer belt 7 is not damaged as a result of depression by the
cleaning blade 92A even if there exists foreign matter adhering to
the inside surface of the intermediate image transfer belt 7.
The cleaning blade 92A forced against the intermediate image
transfer belt 7 scrapes off the residual toner powder and other
contaminants whatever left on the outer surface of the intermediate
image transfer belt 7 while sliding along the outer surface of the
intermediate image transfer belt 7. As the cleaning blade 92A
scrapes off the residual toner from the outer surface of the
intermediate image transfer belt 7 without producing the stick-slip
phenomenon, it is possible to prevent scattering of the toner
powder and minimize contamination of surrounding areas of the
cleaning blade 92A with the toner powder.
In one variation, the cleaning system of the invention may be
applied to an image forming apparatus employing an
endless-belt-type photosensitive member. In this variation, the
cleaning system is adapted to scraping off residual toner powder
from the endless-belt-type photosensitive member. Specifically, a
cleaning blade of this cleaning system is forced via the
photosensitive member against-an outer surface of a roller
(rotating member) on which the photosensitive member is mounted.
Alternatively, the cleaning blade presses against a portion of an
outer surface of the photosensitive member where the photosensitive
member is not supported from its inside surface by the roller with
the cleaning blade held in contact with the photosensitive member
at an acute angle. The cleaning blade of the cleaning system of
this variation and the alternative thereof can scrape off the
residual toner powder from the photosensitive member and prevent
scattering of the toner powder without producing the stick-slip
phenomenon. Furthermore, since this cleaning system can also remove
fine particles of such material as a slip agent and an external
additive attached to toner particles, it is possible to prevent the
slip agent from adhering to a charging wire and suppress
deterioration of image quality.
Furthermore, the cleaning blades 92, 92A of the aforementioned
embodiments may be modified such that the cleaning blades 92, 92A
contain fluoroplastic not only in their surface layers but the
cleaning blades 92, 92A are formed in their entirety of a material
containing fluoroplastic.
The invention being thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
invention.
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